It is known that in the manufacturing of cathode tubes especially adapted to be used on color television receiver appliances, the pre-adjustment of the deflection yoke on its tube is normally made within the plant, so as to obtain the best possible performance of the tube in the appliance.
Briefly, adjustment is either made by automatically or manually controlled machines, thus enabling determination of the optimal position of the deflection yoke on the neck of the tube in order to obtain the best possible image performance of the tube (especially purity of colors and deformations).
Once this adjustment of the yoke on the tube has been made, the yoke is fixed in the determined position. This fixation is usually carried out in one of the following ways:
a. a plastic ring is used which is stuck to the rear of the tube, and then the yoke is fixed, for example, by screws or by glue, onto this plastic ring, after correctly positioning it.
b. rubber wedges or quoins are used that are stuck onto the rear of the tube and onto the yoke, and the yoke is fixed onto the collar tube by metallic clamping means, after the collar has been correctly positioned.
c. mechanical clamping means are used such as screws or similar enabling fixation of the yoke on the tube or on the neck after positioning.
All these means are time-consuming and costly to apply.
According to another technique, reference shoes are provided on the rear of the tube that define the position of the yoke that has been fixed on the neck of the tube by metallic clamping means; this solution demands precision and, thereafter, higher manufacturing costs of the tubes, given that it does not permit a subsequent adjustment of positioning of the yoke.